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| Titel |
CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol |
| VerfasserIn |
G. J. Engelhart, A. Asa-Awuku, A. Nenes, S. N. Pandis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 14 ; Nr. 8, no. 14 (2008-07-24), S.3937-3949 |
| Datensatznummer |
250006296
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| Publikation (Nr.) |
 copernicus.org/acp-8-3937-2008.pdf |
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| Zusammenfassung |
| The ability of secondary organic aerosol (SOA) produced from the ozonolysis
of α-pinene and monoterpene mixtures (α-pinene, β-pinene,
limonene and 3-carene) to become cloud droplets was investigated.
A static CCN counter and a Scanning Mobility CCN Analyser (a Scanning
Mobility Particle Sizer coupled with a Continuous Flow counter) were used
for the CCN measurements. Consistent with previous studies monoterpene SOA
is quite active and would likely be a good source of cloud condensation
nuclei (CCN) in the atmosphere. A decrease in CCN activation diameter for
α-pinene SOA of approximately 3 nm hr−1 was observed as the
aerosol continued to react with oxidants. Hydroxyl radicals further oxidize
the SOA particles thereby enhancing the particle CCN activity with time. The
initial concentrations of ozone and monoterpene precursor (for
concentrations lower than 40 ppb) do not appear to affect the activity of
the resulting SOA. Köhler Theory Analysis (KTA) is used to infer the
molar mass of the SOA sampled online and offline from atomized filter
samples. The estimated average molar mass of online SOA was determined to be
180±55 g mol−1 (consistent with existing SOA speciation studies)
assuming complete solubility. KTA suggests that the aged aerosol (both from
α-pinene and the mixed monoterpene oxidation) is primarily
water-soluble (around 65%). CCN activity measurements of the SOA mixed
with (NH4)2SO4 suggest that the organic can depress surface
tension by as much as 10 N m−1 (with respect to pure water). The
droplet growth kinetics of SOA samples are similar to
(NH4)2SO4, except at low supersaturation, where SOA tends to
grow more slowly. The CCN activation diameter of α-pinene and mixed
monoterpene SOA can be modelled to within 10–15% of experiments by a
simple implementation of Köhler theory, assuming complete dissolution of
the particles, no dissociation into ions, a molecular weight of 180 g mol−1,
a density of 1.5 g cm−3, and the surface tension of water. |
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